See e-mail on dev@:
"[7.0.x] Document is invalid: no grammar found. for MergedWebXml in Jasper"
http://markmail.org/message/jbnbmezbdegoufm5
This issue affects the current TC7 code (7.0.51-dev), since the following commit: http://svn.apache.org/r1552826
It does not affect 7.0.50.
(The error is generated internally, but the list of error is not checked, so it is effectively ignored).
Steps to reproduce:
1. Enable validation, by adding the following line to conf/catalina.properties
org.apache.catalina.STRICT_SERVLET_COMPLIANCE=true
2. Set JAVA_HOME variable to point a Java 6 JDK. I am using 6u45.
3. Start Tomcat
4. Go to http://localhost:8080/
Expected: index.jsp of the ROOT web application
Actual: Error 500, with the following message in localhost.DATE.log file:
08.01.2014 1:20:11 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [] threw exception [org.apache.jasper.JasperException: XML parsing error on file org.apache.tomcat.util.scan.MergedWebXml: (line 2, col 9)] with root cause
org.xml.sax.SAXParseException: Document is invalid: no grammar found.
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:195)
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.error(ErrorHandlerWrapper.java:131)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:384)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:318)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.scanStartElement(XMLNSDocumentScannerImpl.java:250)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl$NSContentDriver.scanRootElementHook(XMLNSDocumentScannerImpl.java:626)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:3104)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:921)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:647)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:140)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:511)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:808)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:119)
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:232)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:284)
at org.apache.jasper.xmlparser.ParserUtils.parseXMLDocument(ParserUtils.java:105)
at org.apache.jasper.compiler.JspConfig.processWebDotXml(JspConfig.java:95)
at org.apache.jasper.compiler.JspConfig.init(JspConfig.java:243)
at org.apache.jasper.compiler.JspConfig.findJspProperty(JspConfig.java:302)
at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:114)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:373)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:353)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:340)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:657)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:357)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:409)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1044)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:662)

The cause of this issue is that Jasper uses DOM parser, while the rest of Tomcat code uses Apache Commons Digester.
When DOM parser is used directly, calling "factory.setValidating(validating);" on DocumentBuilderFactory enables DOM validation only, but not the schema one. (in ParserUtils.java in jasper)
When Digester is used, calling digester.setValidating(true) enables not only DOM validation, but schema one as well.
See Digester#getFactory() for a fragment of code that enables schema validation.
By the way, XmlErrorHandler used by Japser here stores the errors and warnings in a HashSet. In this case, there are 2 errors, and which one is reported is random, as the HashSet has no order. From debugger:
[org.xml.sax.SAXParseException: Document root element "web-app", must match DOCTYPE root "null"., org.xml.sax.SAXParseException: Document is invalid: no grammar found.]

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